DEVICE FOR BENDING PRELIMINARILY FINNED STRAIGHT TUBES Russian patent published in 2002 - IPC

FIELD: heat power engineering; heat exchanger coils. SUBSTANCE: device for bending preliminarily finned tubes when making flat coils of convective surfaces of heat exchanger with fin-free sections of designed length at both sides from top each bend has drive shaft with bending template and swivel carriage rigidly secured on shaft in guides of which saddle is installed which carries clamp (clamping block) for tube to be bent, saddle being shifted by clamp drive, fixed carriage with drive saddle secured in bed frame with drive slider installed in saddle guides for reciprocating along axis of straight section of bending tube, both together with tube and without tube. Width of working impressions of bending template, clamp and pressure slider is equal to outer diameter of finning, and their depth is not less than half of width of impression. Bending template is furnished additionally with insert in form of part of sector of circle whose radius is equal to bending radius of carrying tube. Central angle of insert sector is smaller than designed angle of part of fin-free carrying tube bend and part of insert adjoining vertex of central angle of sector is removed. Insert has working impression on cylindrical part of side surface whose width is equal to outer diameter of carrying tube (without finning), and depth of impression is equal to half of its with. Insert is secured in seat of bending template with provision of concentric arrangement of working impressions of insert and bending template. Thickness of insert lies within the limits of one diameter of carrying tube (without finning) and outer diameter of its finning. Central angle of insert sector is smaller than designed value of central angle of fin-free part of bend of carrying tube within the limits of half value of helix of spiral finning on straight section, and angle between bisecting line of central angle of sector of insert installed in bending template and initial direction of action of clamping force on finned tube in bending template before starting the bending being 90^°. Working impression of pressure slider on part of its length is provided with concentric inner step whose height in impression radius in normal section of impression is equal to height of fin of bending tube and which forms working impression for carrying tube in fin-free zone of future bend at both sides from its vertex. Length of said step is less than half the full length of fin-free straight section of carrying tube in zone of future bend by at least two-three values of fin thickness, and middle of said step along its length in initial pre-bending installed position of pressure slider is located from beginning of bending section of finned part of tube at a distance of S = 0,5πR, where R is radius of tube bending. EFFECT: increased efficiency of heat exchangers using preliminarily finned straight tubes. 5 cl, 2 dwg